1. Field of the Invention
The present invention relates to inducible gene expression constructs and methods of inducing gene expression using a combination of inducing agents.
2. Discussion of the Background
Gene therapy now is thought to be widely applicable in the treatment of a variety of cancers and a number of other diseases. Viral vectors are one method employed as a gene delivery system. A great variety of viral expression systems have been developed and assessed for their ability to transfer genes into somatic cells. In particular, retroviral and adenovirus based vector systems have been investigated extensively over a decade. Recently, adeno-associated virus (AAV) has emerged as a potential alternative to the more commonly used retroviral and adenoviral vectors. Lipid vectors including cationic lipids and liposomes also are used to deliver plasmid DNA containing therapeutic genes.
The therapeutic treatment of diseases and disorders by gene therapy involves the transfer and stable or transient insertion of new genetic information into cells. The correction of a genetic defect by re-introduction of the normal allele of a gene encoding the desired function has demonstrated that this concept is clinically feasible (Rosenberg et al., New Eng. J. Med, 323:570 (1990)). Indeed, preclinical and clinical studies covering a large range of genetic disorders currently are underway to solve basic issues dealing with gene transfer efficiency, regulation of gene expression, and potential risks of the use of viral vectors. The majority of clinical gene transfer trials that employ viral vectors perform ex vivo gene transfer into target cells which are then administered in vivo. Viral vectors also may be given in vivo but repeated administration may induce neutralizing antibody.
A major issue facing potential clinical application of gene therapy is the question of how to heterologous genes expressed in clinically significant quantities in selected tissues of the subject. Gene regulatory elements provide a potential answer to that question. Gene regulatory elements such as promoters and enhancers possess cell type specific activities and can be activated by certain induction factors via responsive elements. The use of such-regulatory elements as promoters to drive gene expression facilitates controlled and restricted expression of heterologous genes in vector constructs. For instance, heat shock promoters can be used to drive expression of a heterologous gene following heat shock.
U.S. Pat. Nos. 5,614,381, 5,646,010 and WO 89/00603, refer to driving transgene expression using heat shock at temperatures greater than 42° C. These temperatures are not practicable in human therapy as they can not be maintained for a sustained period of time without harm to the individual.
Gene therapy could be used in combination with a variety of conventional cancer therapy treatments including cytotoxic drugs and radiation therapies. It has been shown that hyperthermia enhances the cell killing effect of radiation in vitro (Harisiadis et al., Cancer, 41:2131–2142 (1978)), significantly enhances tumor response in animal tumors in vivo and improves the outcome in randomized clinical trials. However, the major problem with the use of hyperthermia treatment is that the hyperthermia system can not adequately heat large and deep tumors.
Likewise, the major therapies currently used to treat cancer include radiotherapy, chemotherapy, hyperthermia and immunotherapy. Gene therapy is emerging as a new treatment for cancer, with encouraging clinical results. With the emerging view of combinatorial therapy as an approach to cancer treatment (Feyerabend et al (1997) Anticancer Res 17:2895–2900; Otte (1988) Eur J Pediatr 32:17–30), there is a need to integrate gene therapy with conventional therapies. Most gene therapy approaches have utilized constitutive expression of therapeutic genes (e.g. co-receptors such as B7.1 and B7.2, cytokines such as IL-2 and GM-CSF) by viral promoters (e.g., cytomegalovirus and Rous sarcoma virus). An alternative method is the use of expression vectors that can be induced to express therapeutic genes by one or more of the aforementioned conventional therapies.
Thus, it would be useful to develop vectors that may be used at temperatures of 42° C. and below, systemically or locally, in conjunction with cancer therapies such as radiotherapy, chemotherapy, hyperthermia, and immunotherapy, to treat a patient such that the expression of the therapeutic gene(s) is activated preferentially in regions of the body that have been subjected to conditions which induce such expression.